The invention relates to an amplifier scheme, and more particularly to an amplifier circuit capable of providing a large or larger actual resistance for its closed feedback loop to completely avoid leakage currents flowing back to input(s) of an amplifier.
For signal processing, a conventional scheme may adopt a conventional AC-coupled amplifier or a conventional DC-coupled amplifier to process an input signal with a programmable gain. For implementation, an input capacitor at the input of the conventional AC-coupled amplifier corresponds to a very large capacitance and is usually placed on an external printed circuit board but not included within the integrated circuit of the amplifier, which is not cost-effective. To solve the problems of conventional AC-coupled amplifier, the conventional DC-coupled amplifier adopts a different circuit structure in which its gain is determined based on the input capacitance and a feedback capacitance, and thus the input capacitance can be designed to become smaller.
However, the conventional DC-coupled amplifier circuit has leakage currents flowing through its feedback resistors back to input(s) of an amplifier of the conventional DC-coupled amplifier circuit, which inevitably causes that the actual resistances of its feedback resistors decrease and become smaller than the resistances designed by user(s). This will be a more serious problem when the resistances are designed to be a larger value by the user(s) for some application fields such as audio signal processing.